To investigate the health of vessels or organs in the human body (e.g., cardiac vessels), it can be important to be able to measure certain internal characteristics or parameters of those vessels or organs, which can provide details related to cardiac diseases and ailments so that appropriate treatment can be performed. Traditional methods for measuring dimensions of vessels or organs include intravascular ultrasound (“IVUS”) or optical coherence tomography (“OCT”). In both cases, a source of energy (ultrasound or coherent light) and a scattering sensor (for ultrasound waves or light) are mounted on a catheter and rotated along the axis of the body lumen in order to scan the inside of the lumen and map out its profile, revealing its cross-sectional area. These methods, however, are either very expensive and/or are cumbersome. For example, the use of IVUS requires advancing the ultrasound catheter to a target area, such as a lumen, obtaining the information, removing the catheter, combining the information obtained using the catheter with an angiogram to provide parameters about the vessel, then proceeding with a medical procedure such as, for example without limitation, a stent delivery procedure. In addition to the costs and time disadvantages, these procedures are also inconvenient to the patient.
Electrode-based interventional instruments have been explored as alternatives to IVUS and OCT techniques. Some approaches have used catheters with two electrodes disposed thereon for determining the cross-sectional area of a blood vessel. In use, the catheter is advanced through the blood vessel to a measurement site, and an AC voltage is applied to the electrodes, producing a current through the blood within the vessel. The impedance is measured. A fluid is then injected into the lumen to replace the blood with the fluid, and a second impedance measurement is taken. The multiple impedance measurements are then used to determine the cross-sectional area of the blood vessel between the electrodes. In order to use these catheters in conjunction with an angioplasty procedure, the catheter is first advanced to the treatment site to perform a measurement of the vessel cross-section. The measurement device is then withdrawn and a balloon catheter is advanced to the obstructed site in order to perform the dilatation. Since both the measurement device and the dilatation catheter can be difficult to advance to the obstructed site, multiple device exchanges have to be made adding more time and complexity to the procedure.
A dimension-sensitive angioplasty catheter having an inflatable balloon and a plurality of vessel-measuring electrodes has also been described. The electrodes are mounted on the surface of the catheter tube and are individually connected to the proximal end of the catheter. The catheter also includes an inelastic balloon. The balloon is adapted to be inflated through the introduction of a suitable fluid into the lumen of the tubular member to press the stenotic lesion against the vessel wall. One pair of electrodes is selected for connection to the output of an oscillator, and a second pair of electrodes is selected for sensing a signal that results from conduction through the blood in the vessel. The technique requires injection of fluid into the expander with known concentration at the time of making the measurements using the electrodes, thus adding to the complexity of the procedure. The measurement may also need to be timed with the fluid injection creating room for inaccuracies and procedural complexity. The repeatability of measurements may be affected if the injected fluid does not clear out the blood completely in the vessel at the time of the measurements.
A need therefore exists for improved systems and methods for accurately measuring lumen parameters, such as in the cardiac vasculature.
Additionally, typical imaging techniques provide very limited information, especially about blood vessels and the heart. For example, an angiogram, which uses X-Ray imaging modality and a contrast agent injected into the blood vessel, provides a simple two-dimensional snapshot of the blood vessels. These snapshots or images are used to guide a physician during invasive procedures that are needed for a variety of treatments related to coronary conditions. For example, stent deployment to unblock an artery involves introducing a guide wire and a stent delivery catheter along the aorta to the point of the expected block, and the stent is subsequently deployed. This procedure relies heavily on the skill of the physician operating the devices. Typically, the blood vessel can be tortuous and have turns that may not be evident in a 2-D snapshot. The operators rely on their experience and make educated estimations based on the 2-D images to position the stent before deploying it. This can lead to inaccurate placements and hence less than ideal treatment. To get more accurate positional information it may be useful to obtain a three-dimensional rendering of the lumen trajectory.
Some approaches have attempted to generate three-dimensional (“3D”) images of flow structures and their flow lumen using ultrasound technology. For example, some approaches have used multiple 2D slices to generate a 3D image. These techniques are specific to ultrasound imaging techniques, and hence require additional equipment to achieve the outcome.
Some approaches use a method of obtaining at least two complementary images to differentiate the structures and the functions in the region such that image segmentation algorithms and user interactive editing tools can be applied to obtain 3D spatial relations of the components in the region. At least two complementary methods of imaging can be used (e.g., CT and MRI) from which two images are obtained based on identifying existing known anatomical features. The two images then are used together to form a high resolution 3D image.
Some approaches use a method for reconstructing 3D data records from endo-lumen 2D section images of a hollow channel, especially a blood vessel, using an image providing an endo-lumen instrument such as a catheter. 2D images of the hollow channel are prepared and by considering a known relative displacement position of the instrument in the hollow channel for each 2D sectional image a 3D image data record is reconstructed by computer from the image data of the 2D sectional images. The described technique requires multiple 2-D images for a single section of the hollow channel.
Some approaches use an instrument that is moved in a lumen at a defined speed over a defined distance. The approaches intraluminally record 2D images and create a 3D image.
Known techniques require multiple images be made available to obtain a 3D lumen assessment and visualization. Further, in some instances, to obtain lumen trajectory in a 3D volume, complete procedural changes may be necessary, which may not be conducive for adaptation with existing techniques. Also, the imaging procedures described may be cumbersome and complex, and consequently, the medical procedure requires modification to accommodate the imaging procedure, which sometimes is impractical. There are still needs for methods and devices that can provide 3D trajectory of the blood vessel accurately and in a reasonable amount of time to enable a skilled operator to perform intricate invasive procedures with greater confidence.
Imaging vascular lumens is, in general, performed using several types of endo-lumen instruments, such as Intra Vascular Ultrasound (“IVUS”), Optical Coherance Tomography (“OCT”), Near Infrared spectroscopes (NIR), and other lumen measurement instruments. Typically these endo-lumen measuring techniques provide important parametric information that aids a practitioner in clinical decision making. For example, an IVUS catheter is used to image the lumen and determine the parameters such as Cross Sectional Area (“CSA”) of lumen. The practitioner uses this information to make clinical decisions when, for example, determining an appropriate size of a stent to be delivered in the subject.
This parametric information is not, however, co-registered with the imaging modality used, for example, an X-Ray modality. The corresponding positions where the parameters were measured are not preserved for further use. The physician has to estimate and guide the therapy endo-luminal devices to the points of interest (such as areas of minimum cross-sectional area where a stent is to be deployed).
There have been efforts to fuse images obtained from two or more imaging modalities to locate the position of the endo-lumen instruments vis-á-vis the image of the heart or the artery. In this respect, the focus so far has been to be able to reconstruct a 3D image of the lumen or create a guidance system by using two or more imaging modalities. However, none of these applications address the co-registering of parametric information with the positional information of the endo-lumen instruments.
US 2011/0019892 provides a method for visually supporting an electrophysiological catheter application. An electroanatomical 3D mapping data of a region of interest in the heart is visualized. A 3D image data of the region of interest is captured before the catheter application. A 3D surface profile of objects in the region of interest is extracted from the 3D image data by segmentation. The electroanatomical 3D mapping data and 3D image data forming at least the 3D surface profile is assigned by registration and visualized by superimposing on one another. Characteristic parameters are measured for catheter guidance during the catheter application. The characteristic parameters are compared with at least one predefined threshold value and regulation data for catheter guidance is generated as a function of the comparison result. The regulation data is integrally displayed and represented in the superimposed visualization. The technique described herein presents complexity in terms of first having a 3D map of a region of interest, then obtaining 3D image of region of interest, then segmenting the 3D image to obtain a 3D profile of region of interest and then superimposing on the 3D map. The characteristic parameters are obtained separately by use of a catheter. A threshold value is used to compare with the characteristic parameter and then regulation data for catheter guidance is obtained and displayed. The technique is complex and uses threshold value to provide some regulation data for catheter guidance. The technique, however, fails to co-register the parametric information with the positional information for accurate guidance for medical procedures.
US 2009/0124915 describes a method for guidance to an operator to position electrodes upon a segmented heart model (“SGM”). The SGM is included in a map panel on a display screen. A catheter advanced into a beating heart supports one or more electrodes. During a single beat of the heart, an image is obtained with darkened portions corresponding to locations of the electrodes. The image is presented in the same map panel as the SGM. The current location of the electrodes is confirmed relative to the SGM, either manually or through automated software algorithms. Electrophysical (EP) data is captured that represents electrophysiological signals of the beating heart at the current location for each of the electrodes. A signal processing algorithm is applied to the captured EP data in view of the confirmed current location of the electrodes to result in a calculation that is mapped at the confirmed location of the electrodes. This technique uses a modeling approach where the catheter is tracked through fluoroscopy guidance and imaged, and the tracked image is used to determine the position of catheter electrodes on the previously selected model for the heart. The corresponding EP data is then mapped across the locations on the model. The technique provides both computational complexity and again uses a pre-selected model for registering the EP data. Mapping on a pre-selected model can lead to errors as the heart is in dynamic motion at any given time and the model may not represent the current state for the images heart
As mentioned herein above, the diagnostic devices (IVUS, OCT, NIR, other lumen assessment devices) used in the vascular spaces (coronary, peripheral, renal, abdominal aorta, neurovascular, etc.) provide diagnostic parameters but do not integrate this information with the position of the devices with respect to a reference so that other diagnostic or therapeutic devices can be guided to the region of interest. Therefore there is continued need in the art to assist the medical practitioner in providing relevant information leading to a more effective therapy.